OBJECTIVE Our goal was to evaluate whether treatment of bacterial vaginosis during pregnancy with 2% clindamycin vaginal cream reduces the incidence of either preterm delivery or low birth weight or of both. METHODS A multicenter, double-blind, randomized, placebo-controlled trial in Indonesia compared a 2% clindamycin vaginal cream with a placebo cream. Women seeking prenatal care at 14 to 26 weeks of gestational age who had bacterial vaginosis (Gram stain score > 6 and pH of vaginal fluid > 4.5) were invited to participate. Of the 745 women enrolled, 681 (91.4%) women were followed up through delivery. RESULTS Clindamycin vaginal cream was an effective treatment for bacterial vaginosis. Two weeks after completion of the treatment, 85.5% of the women were cured. The rate of preterm delivery (< 37 weeks) was 15.0% for clindamycin patients and 13.5% for placebo patients (odds ratio 1.1, 95% confidence interval 0.7 to 1.7). The rate of low birth weight was 9.0% for clindamycin patients and 6.8% for placebo patients (odds ratio 1.3, 95% confidence interval 0.8 to 2.4). CONCLUSIONS Treatment of bacterial vaginosis with clindamycin vaginal cream did not reduce preterm delivery or low birth weight. Although clindamycin vaginal cream is an effective treatment for bacterial vaginosis, intravaginal treatment would not be effective against bacterial vaginosis-associated microorganisms harbored in the upper genital tract. Systemic treatment may be required to eradicate upper tract infection to reduce preterm delivery.